In a carburetor associated with an engine mounted on a motorcycle or the like, when the outside temperature is low, starting capability of the engine may be deteriorated. This is because the interior of the intake path is excessively cooled in cooperation with the fact that evaporation heat is absorbed by ambient air when fuel is evaporated.
As a countermeasure for solving such a problem, an exemplary heating device for a carburetor of the background art as shown below is disclosed in Japanese Utility Model Laid-Open No. 5326/1996, the entirety of which is hereby incorporated by reference. The heating device for a carburetor stated in this publication heats the carburetor by introducing a portion of the engine cooling water that is circulating between the engine and the radiator by the cooling water pump after it has passed through the engine.
More specifically, the pump is the device for introducing engine cooling water after cooling the engine and thus heated as appropriate through the carburetor heating piping system diverged from the radiator piping separately from the radiator piping system passing through the radiator to the carburetor and heating the same. Engine cooling water flowing through the carburetor heating piping system is passed through the carburetor, joined with engine cooling water from the radiator piping system, introduced to the suction side of the cooling water pump, and then fed again to the engine side through the cooling water pump for circulation.
The radiator piping system is provided therein with a thermostat valve that is “closed” when the temperature of engine cooling water is low, and “opened” when the temperature is high. In addition to the heating device for a carburetor disclosed in the aforementioned publication, another type is known in the background art in which the extremity of the carburetor heating piping system using engine cooling water is returned to the radiator piping that connects the thermostat valve and the radiator.
The present inventors have determined that the background art suffers from the following problems. In former heating device(s) for a carburetor, since the extremity of the carburetor heating piping system is returned to the suction side of the cooling water pump, engine cooling water is always circulating in the carburetor heating piping system while the cooling water pump is in operation. Engine cooling water is always present irrespective of whether the thermostat valve is opened or closed. Accordingly, the carburetor is continuously heated even after the temperature around the carburetor such as the engine or the like is increased, which may result in lowering of system efficiency.
In order to deal with this problem, former heating device(s) for a carburetor have been provided with a switching valve that “opens” when the temperature of engine cooling water is lower than a prescribed value, and “closes” when it is higher than that value. Therefore, the heating device for a carburetor is prevented from being operated when the temperature of engine cooling water exceeds a prescribed temperature.
In former heating device(s) for a carburetor, when operating the carburetor heating piping system only when the engine is started, there arise problems in that a special switching valve must be provided and the corresponding costs increase. In addition, reductions in system size become difficult and the possibility of limitations on the freedom of design increase since a space for mounting the switching valve must be secured. In the second heating device for a carburetor described above, when the thermostat valve is closed, engine cooling water in the radiator piping system and engine cooling water in the carburetor heating piping system barely circulate.